Optical semiconductor elements, such as light emitting diodes (LED), are used as indicators or light sources. Recently, their outputs have become higher and their wavelengths have been shorter, which causes a problem that resin materials present near the optical semiconductor elements are degraded due to light to turn yellow, resulting in lower light output.
The following Patent Literature 1 discloses, as a resin composition for encapsulating optical semiconductors, an epoxy resin composition in a B stage which comprises an epoxy resin, a curing agent, and a curing promoter. It describes that bisphenol A epoxy resin or bisphenol F epoxy resin is mainly used as the epoxy resin and triglycidyl isocyanate may be used. However, the afore-mentioned composition has the aforesaid yellowing problem, particularly when an optical semiconductor element is turned on at a high temperature or for a long time.
Patent Literature 2 discloses a composition which comprises an epoxy resin derived from isocyanuric acid, as a heat-resistant and light-resistant epoxy resin composition for encapsulating light emitting elements. However, light resistance of the composition is insufficient, again.
Meanwhile, recently, sizes of molded package have become bigger, for instance, in Matrix Array Package (MAP) method and, therefore, warpage in curing of an encapsulating resin has become a serious problem. Large warpage causes various problems in a package transfer step or a package cutting step. The afore-mentioned compositions are unsatisfactory also in this respect.
Patent Literature 1: Japanese Patent Application Laid-Open Hei-02-189958
Patent Literature 2: Japanese Patent Application Laid-Open 2005-306952